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Helicoils in tight spots/other practical ways to repair corroded alumi


gazelle
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This is a practical question of how do I helicoil in a tight spot

I have an aluminium bodied electric windlass on a yacht which has a stainless chain shedder (9 in the diagram below )that used to be held on the body by stainless steel screws (34). With the addition of salt water the inevitable has happened and the holes have opened up by corrosion (Lots of white powder, bigger holes) and the screw have dropped out. To give an idea of scale, the aluminium casting is 205mm high, 242mm wide and 295mm long.

post-3070-1237978366_thumb.png

So two questions (which can also apply to LR's so thereby some possible LR content ;) ):

  • With the tight space between the bottom and the vertical plate, which is where the helicoils would need to go to replace the original material, how do you apply the tap? The handle would just get in the way!
    Is there another way to reattach the chain shedder that you can suggest?

Sorry about this being OT. However the knowledge of the people on here is very relevant to the materials and techniques.

Martin

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Is there anything on the other side of 10? Would some long bolts go right through?

Failing that, is there enough material below the holes to allow a helicoil?

It's always struck me as odd that anything is made of ali in a marine environment......

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Is there anything on the other side of 10? Would some long bolts go right through?

Failing that, is there enough material below the holes to allow a helicoil?

It's always struck me as odd that anything is made of ali in a marine environment......

Inside 10, just behind the screws is the motor shaft - so at this location we cannot use bolts through. it is just visible below the cover (10) in the picture. 22 is the bearing surface that is inside the top of the cover.

The holes can be raised a few mm to allow the helicoil to be inserted, but not far.

The Ali is OK on its own above the water in a seawater enviroment. It's just that it gets used with steel fixings that causes the problems!

Martin

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Looking at the image I think you are saying that the helicoil tap handle would not have the clearance to turn all the way round? I made an adaptor to extend mine. A bit of square tube welded onto an old 3/8 drive socket and I then used my socket set T bar.

The next problem could be that the holes are not deep enough to tap fully and you then may not get enough turns of helicoil in there. Then there may be clearance problems if the first turn of the helicoil, the bit the insert tool locates on, can't be knocked off and that could also shorten an already short hole.

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Looking at the image I think you are saying that the helicoil tap handle would not have the clearance to turn all the way round? I made an adaptor to extend mine. A bit of square tube welded onto an old 3/8 drive socket and I then used my socket set T bar.

The next problem could be that the holes are not deep enough to tap fully and you then may not get enough turns of helicoil in there. Then there may be clearance problems if the first turn of the helicoil, the bit the insert tool locates on, can't be knocked off and that could also shorten an already short hole.

That is correct.

If Helicoils are likely to give problems, are there any other ways of reattaching the steel plate? Would Epoxy or sikaflex be strong enough for example?

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What about drilling and tapping one size bigger then use Aluminium bolts. The bolts will corrode in contact with the SS - but they are easier to replace.

You could even use Nylon bolts?

Helicoils will fix the problem - but only temporarily. It will not gain you anything over the above.

Also, get the Aluminium part Anodized - it helps a lot with electrolytic corrosion.

Si

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If possible tap one size up and use larger bolts.

Or

Use Keenserts which are a little like helicoils but are easier to fit and require no special tools.

But whatever you use make sure you fit the insert and the bolts using Duralac which will prevent corrosion in the future.

Steve

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If your chain and gypsy are a little worn then you will get away without a chain shedder at all (I've always called it a finger...) If they are a good match though the gypsy will grab the chain and wrap it into an impossible knot.

Another vote for drilling and tapping one size bigger. Use Duralac on reassembly and high grade stainless bolts.

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If your chain and gypsy are a little worn then you will get away without a chain shedder at all (I've always called it a finger...) If they are a good match though the gypsy will grab the chain and wrap it into an impossible knot.

New chain - and it does grab!

Thanks guys, I will have a look when I get there and see what I can do. Drill and tap seems to be the order of the day, (with and insulator between the bits).

Martin

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Oh - forgot - you don't need a tap wrench, just use an open ended spanner on the end of the tap and hold it in alignment with your finger as you start it off.

That will get as close in as it is possible to get.

Si

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  • 4 weeks later...

Thanks for all you help guys. When I got to look the holes they were too big for a drill/retap. (Could not access before as the cluck plate had seized - LR no 1 tool un-seized it for me)

post-3070-1240222244_thumb.jpg

Looking around for other solutions, I decided to clean out the holes and fill with epoxy. Before the epoxy set, the screws were put in. I will let you know how it fares.

Note the clever use of materials in this location (in a location that gets dunked in salt water regularly) - Ali winch body, Stainless drum and shedder, galvanised steel chain...... ;)

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  • 1 month later...

Right Chemical Metal was a waste of time and effort. Not sure when it fell out, but it was not long after it was first used.

Never mind.

Now looking to drill and tap several sizes bigger.

No for the innocent question:

If I want to tap for a m5, m6, m7 or m8 bolt, then what size drills do I need to use(on site with a unsupported electric drill)?

Duralac and open ended spanners......

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Right Chemical Metal was a waste of time and effort. Not sure when it fell out, but it was not long after it was first used.

Never mind.

Now looking to drill and tap several sizes bigger.

No for the innocent question:

If I want to tap for a m5, m6, m7 or m8 bolt, then what size drills do I need to use(on site with a unsupported electric drill)?

Duralac and open ended spanners......

Drill sizes for metric taps

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As said above i'd consider a couple of alternatives,

Go bigger as to helicoil you'll have to anyway and/or drill and tap from the back if you have more access.

As for no room for a tap wrench either use an open ended spanner, a long tap or tap extension or a ratchet tap wrench altho these tend to be fairly large dia's

Mark

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can you just make a new chain sheeder that is bolted to the bottom plate instead of the vertical surface?

As a side, if you are trying to use epoxy on aluminium you need to remove the oxide layer, and remeber that aluminium is so reactive that this layer forms instantly in air... one way of doing it is mixing the epoxy, apply it to the clean metal and then use sand paper or another abrasive to take off the oxide layer, the epoxy will stop it oxidising

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